<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        function countDown(time){
            var nowTime = +new Date(); //返回当前时间的总毫秒数
            var inputTime = +new Date(time);//返回用户输入时间的总毫秒数
            var times = (inputTime - nowTime) / 1000;//剩余时间的总的秒数
            var d = parseInt(times / 60 / 60 / 24);//天
            d = d < 10 ?'0'+ d : d;
            var h = parseInt(times / 60 /60 % 24);//时
            h = h < 10 ? '0'+h:h;
            var m = parseInt(times / 60 % 60);//分
            m = m < 10 ? '0'+ m : m;
            var s = parseInt(times % 60);//秒
            s = s < 10 ? '0'+ s : s;
            return d + '天' + h +'时'+ m +'分'+ s +'秒';
        }
        console.log(countDown('2021-3-5 18:00:00'));
    </script>
</head>
<body>
    
</body>
</html>